Amblyopia and visual development
Amblyopia is a neuro-developmental condition in which vision does not develop adequately in one eye. In the early years of life, there is a constant process occurring in our brains where neurons, or nerve cells, are forming connections with other neurons. This describes the basic units of information processing.
Every baby is born with approximately 100 billion neurons. The number of possible connections or synapses formed between neurons in an infant’s brain is amazing.
At birth, a baby has 50 trillion connections or synapses. In the first three months of life, the synapses multiply more than 20 times. By the end of the first year, the brain has 1,000 trillion synapses. It is the development of these connections which allows us to see, hear, smell, taste and move.
For example, the optic nerve of the eye has millions of connections with the visual cortex of the brain. Just as the quality of the picture we see on a television screen relies on the signal from the antenna, the image processed by the brain is dependent upon the image received and transmitted by our eyes.
Connections that are used regularly become stronger and more complex, those that are not used are “pruned” and eventually eliminated. With lack of appropriate visual stimulation, the connections between the eye and the brain may fail to develop; as a result, the eye fails to develop the ability to see clearly, this is known as Amblyopia.
Any condition that affects normal visual development can cause Amblyopia. It can be caused by strabismus, which is an imbalance in the positioning of the two eyes. The presence of an eye turn has the potential to cause double vision. As double vision is so disconcerting, the child’s brain overcomes this by ignoring the image seen by the turned eye (this is known as suppression).
Most children adapt well to seeing through one eye; because of this many parents are unaware of the problem until it is diagnosed during a thorough eye examination. Amblyopia can also occur in eyes that are straight, but have significant or unequal refractive errors. Amblyopia can be caused when one eye is either more myopic (nearsighted); hyperopic (farsighted), or astigmatic (distorted image) than the other eye. The affected eye does not receive proper visual stimulation; therefore, normal vision does not develop.
Amblyopia affects many areas of vision including the ability to see clearly. Recognising shapes and discriminating fine details and differences; focusing on close work and the ability to move the eyes in a fluid and precise manner; along with the ability to make accurate judgements of surrounding space are often affected.
The spatial effects of Amblyopia include poor depth perception, peripheral awareness, posture and balance. Confidence in climbing activities, playgrounds, steps and stairs, bike-riding, ball skills and road sense may be reduced.
In the classroom, the ability to see the board and small print will be more difficult.
Writing posture, neatness and page organization may be irregular. Copying skills will often be slower and visual attention is more susceptible to being distracted. Eye movement and tracking skills are often less controlled, causing excessive head movement and leading to decreased fluency, along with problems keeping focus on a page covered in print.
Writing posture, neatness and page organization may be irregular. Copying skills will often be slower and visual attention is more susceptible to being distracted. Eye movement and tracking skills are often less controlled, causing excessive head movement and leading to decreased fluency, along with problems keeping focus on a page covered in print.
Treatment of Amblyopia
The key to the management of amblyopia is identifying the condition as early as possible since neural pathways are more plastic or modifiable during the infant years. It is important to institute therapy as early as possible, as the later therapy is implemented, the worse the prognosis.
Treating amblyopia requires the child to use the amblyopic or weaker eye. Common forms of amblyopia therapy include:
Spectacles
Assessment of eye health through a through eye examination, is essential to ascertain the long term chances of improvement and allow our optometrists to identify the best treatment options.
A spectacle or contact lens prescription improves visual clarity to the optimum level. This is the first step required to initiate a change in visual status.
Spectacles are also able to help and sometimes fully straighten a turned eye, especially if the child demonstrates a significant degree of hyperopia (long-sightedness).
Eye Patching
An opaque, adhesive or specific optical patch is worn over the stronger eye. This therapy forces the child to use the amblyopic eye, thus stimulating the visual brain centres. Eye patching is not an instant cure and is likely to go on for some months. It is important to realise that in order for patching to be successful it needs to include activities that stimulate vision, not just passive viewing tasks such as watching TV. This can include exercises to improve focusing, eye tracking, spatial awareness, and eye-coordination.
In pre-school children, it is more common to patch the stronger eye all day. In school age children; good visual outcomes are achieved with two hours of patching per day, whilst performing activities to stimulate the weaker eye’s attention. A schedule of five out of seven days per week is often very effective.
The range of activities that stimulate vision when the eye is patched, include the following:
Improve lighting (natural or artificial), as well as the size, contrast, borders, colour and detail of any visual objects in the persons environment. e.g. mark path edges, steps, etc. with dark or contrast borders.
Utilise balls or toys with strong geometric patterns.
Use contrast for written tasks such as black or dark blue on white marker-boards, and white or yellow on black chalkboards.
Use large print books, large print playing cards and larger fonts for near tasks and computer activities.
Add distinct borders to the edge of worksheets (particularly to the left), this guides awareness of writing from left to right. Darkening page-lines in workbooks will also be of benefit.
Use strong colours and clearly demarcated shapes for threading, cutting and colouring.
Atropine
Atropine is a drop used to blur the vision in the stronger eye so that the child is encouraged to use the amblyopic eye. Again this treatment works most effectively when it is used concurrently with vision therapy. Atropine can be prescribed by suitably trained health care professionals such as our optometrists.
The duration of any treatment can be weeks to months depending upon many factors such as the child’s age, the degree of vision impairment or whether the amblyopia is related to an eye turn.
Vivid Vision Therapy
Depending on the outcome of the results and the age of the child, additional vision therapy may be recommended. The Vivid Vision therapy system uses a virtual reality environment to stimulate the amblyopic eye and to fine-tune vision development.
